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Biomedical subjects

J Wegmann

Publications and source records attributed to J Wegmann.

7 recordsLinked to original sources
PubMed2001

Poly(ethylene-co-acrylic acid) stationary phases for the separation of shape-constrained isomers.

A new approach for the synthesis of long alkyl chain length stationary phases for use in reversed-phase liquid chromatography is described. Poly(ethylene-co-acrylic acid) copolymers (i.e., (-CH2CH2-)x[CH2CH(CO2H)-]y) with different levels of acrylic acid were covalently bonded to silica via glycidoxypropyl or aminopropyl linkages. 13C cross polarization magic angle spinning (CP/MAS) nuclear magnetic resonance (NMR) spectroscopy was used to characterize the new reversed-phase materials. Aspects of shape selectivity were evaluated for six different columns with Standard Reference Material (SRM) 869a, Column Selectivity Test Mixture for Liquid Chromatography. Selectivity for isomer separations was enhanced for stationary phases prepared with poly(ethylene-co-acrylic acid) containing a mass fraction of 5% acrylic acid. The relationship between alkyl conformation and chromatographic properties was studied by 13C magic angle spinning (MAS) NMR measurements, and correlations were made with the composition of the polymer. Finally, the effectiveness of this phase is demonstrated by the separation of several beta-carotene isomers.

Acrylic Resins↗
PubMed2000

New stationary phase for liquid chromatography with chemically bonded pinane ligand: synthesis and characterization by nuclear magnetic resonance and high-performance liquid chromatographic investigations.

A new bicyclic phase for liquid chromatography was prepared by solution polymerization approaches. To introduce a C4 spacer the starting molecule 3-formylpinane was reduced to the alcohol followed by a substitution of the hydroxy group through a bromide. The obtained halide reacted with magnesium and allyl bromide to the 3-(but-3'-enyl)pinane which was hydrosilylated with trichlorosilane and finally immobilized to silica gels with different pore sizes using the technique of solution polymerization. To elucidate the structure of 3-(but-3'-enyl)pinane high-resolution two-dimensional nuclear magnetic resonance (NMR) spectra were carried out. The new phases were characterized, on the one hand by employing 13C and 29Si solid-state NMR spectroscopy and on the other hand, by separating a standard test mixture consisting of mainly monosubstituted aromatic compounds. The results achieved in chromatography were correlated with the information gained from 29Si CP/MAS NMR measurements.

Bicyclic Monoterpenes↗
PubMed2000

Characterization of polyalkylvinyl ether phases by solid-state and suspended-state nuclear magnetic resonance investigations.

Pure organic polyalkvlvinyl ether phases were synthesized by suspension polymerization using different ratios and compositions of n-butylvinyl ether (C4VE) and n-octadecylvinyl ether (C18VE) with triethylene glycol divinyl ether or divinylbenzene as crosslinkers, respectively. These phases were investigated by means of solid-state 13C cross-polarization magic angle spinning nuclear magnetic resonance (NMR) spectroscopy and 1H high-resolution magic angle spinning (HR MAS) NMR spectroscopy in suspended-state. A comparison of these two methods showed the substantial advantages of 1H HR MAS NMR measurements. Structure elucidation was achieved using a 2D H,H-COSY NMR experiment performed under MAS conditions enabling full peak assignment of the 1H NMR spectra of these phases. The dynamic behavior of the polyalkylvinyl ether phases was determined by employing temperature-dependent measurements of spin-lattice relaxation times (T1) as well as accumulation of a 2D wide line separation NMR spectrum.

Magnetic Resonance Spectroscopy↗
PubMedDate not supplied

Visual and verbal metaphors among children with typical language and language disorders.

Twelve children with language disorders and 12 control subjects were presented with a series of 24 photographic plates from the Metaphoric Triads Test and asked to explain all possible pairings. They also performed a similar task, matched for content, using verbally prepared stimuli. For each trial, one pairing had been designed to make highly probable a metaphoric pairing. Control subjects provided significantly more metaphoric accounts of pairings than children with language disorders, regardless of modality. In addition, photographic plates elicited significantly more metaphoric pairings than verbal preparations. No significant interactions were observed. The findings are discussed from the perspectives of (1) generalized symbolic function and (2) verbal mediation function. The authors call for more research on the role of verbal mediation in metaphoric reasoning.

Child↗